Brownells now makes lightweight AR-15 bolt carrier groups. While the bolt itself is a standard one, the bolt carrier has been lightened by cutting and machining out the material and leaving just enough to make it functional. As a result, the new BCG weighs 8.2 ounces.
The new Brownells lightweight bolt carrier is machined out of 8620 tool steel. The bolt is made of 9310 steel and is also magnetic particle inspected (MPI). The M16 notch is still retained on these bolt carriers in case if you have a lower receiver with a fun switch. The forward assist notches are also retained.
This BCG is advertised to reduce the felt recoil. It may also be a useful part for lightweight AR builds. According to Brownells, the new BCG is compatible with 5.56x45mm NATO/.223 Remington, .300 Blackout and .204 Ruger calibers. I assume that it will work with many other cartridges with .378 rim diameter, too. However, because the manufacturer specifies only these calibers and because this is a non-standard part (despite being a drop-in one), it is probably a good idea to contact the manufacturer and make sure that the BCG is also compatible with the caliber you are going to use it with.
The new Brownells lightweight bolt carrier group comes completely assembled. It has an O-ring in the extractor mechanism as well as properly torqued and staked gas key. These BCGs are available with black nitride, titanium nitride (TiN) or nickel boron finishes. They are already available for purchase on the Brownels website. Right now the MSRP of the black nitrided version is $119.99 and the BCGs with TiN and nickel boron finishes have an identical price tag of $139.99.
Images from www.brownells.com